2. Automatic,involuntary,spontaneous all mean not under the control of the will. That which is automatic, however, is an invariable reaction to a fixed type of stimulus: The patella reflex is automatic. That which is involuntary is an unexpected response that varies according to the occasion, circumstances, mood, etc.: an involuntary cry of pain. That which is spontaneous arises from immediate stimuli and usually involves an expression of strong feeling: a spontaneous roar of laughter.

"self-acting, moving or acting on its own," 1812, from Greek automatos, used of the gates of Olympus and the tripods of Hephaestus (also "without apparent cause, by accident"), from autos "self" (see auto-) + matos "thinking, animated" (see automaton). Of involuntary animal or human actions, from 1748, first used in this sense by English physician and philosopher David Hartley (1705-1757). In reference to a type of firearm, from 1877; specifically of machinery that imitates human-directed action from 1940.